Protecting electric motors.



e. A. URNHAML. PROTECTING ELEGTRIG 'MGTORS. APBLIOA'TION FILED MAR. 89,-1911.

1,063,179 K Patented June 3, 1913.

@Hozumgd I if v ensues Aucrtsrus scanners,

OF CLIFTONDALE, MASSACHUSETTS, ASSIG-NGR SEARS B. C(DNDIT, JR., 0F BROOKLIIQ'E, MASSACHUSETTS.

PROTECTING ELECTRIC TJIOTORS.

Specification of Letters Patent.

Patented June 3, 19113..

Application filed March 30, 1911. Serial No. 817,806.

To aZZ whom 2'25 may concern Be it known that I, GEORGE A. BURNHAM, a citizen of the United States, residing at Cliftondale, in the county of Essex and State of Massachusetts, have invented certain new and useful Improvements in Protecting Electric Motors, ofwhich the following is a full, clear, and exact specifica tion.

This invention relates to the protection of counter electromotive devices. Apparatus of this kind, when out into an electric circuit, takes excessive current. To this class belongs electric motors which, when thrown into a circuit, draw such heavy current as often to damage the windings, particularly on starting under heavy load, unless special protective starting devices are employed. The heavy starting current of such devices is also troublesome in tripping the automatic circuit breakers commonly employed to open the circuit under dangerous running conditions. The circuit breakers are set at a point of calibration where the trip coil- Will operate on a certain definite overload and the low impedance of the armature often permits flow of current exceeding the tripping point, and thus causes the circuit to be broken when unnecessary, since the 39 motor will withstand an excessive overload for a brief starting period. Motors are therefore usually provided Wit-h rheostats or other apparatus to reduce the current at the moment when they are starting until the-motor acquires a suiiiciently. high speed to set up a substantial counter electromotive force to the line potential. lhese objections apply to both direct and alternating current motors.

It is the object of my invention to provide not only for the starting of motors by inexpensive apparatus but also to protect it against overload and underload conditions n the circuit, or open phase conditions in an alternating current circuit, so that on ab normal load variations the motor will be automatically out out of the circuit.

My invei tion is particularly adapted for use with alternating current motors, but may also be applied to direct current motors, and to counter electromotive devices in general where the normal operatin current is much smaller than the current ollowing a closure or" the circuit. I secure protection for the rnotor by employing a combined overload and underload relay coi'itrolling a trip coil of the circuit breaker which cuts the motor into or out of the circuit, the relay being so organized that in its open circuitposition it raises the calibration of the overload member, thus preventing the trip the circuit breaker latch. I further arrange the operating mechanism coil from releasing of the circuit breaker so that the line switch supplying the motor will be closed before the handle or operating; element has reached the full limit of its no vement.

Th various features of novelty will be hereinafter more fully described, and will be definitely pointed out in the claims.

in the accompanying drawing, which illustrates the invention, 1 represents an induc tion motor, and 2 the automatic circuit breaker for cutting the motor into the circuit.

3, i, 5 representthe leads from a supply circuit carrying alternating current.

6 represents the trip coil or release magnet of the circuit breaker, this trip coil being in'a branch circuitconnecting one of the motor leads as 7 with the trip .coil and v with the points of a switch or bridging contact S on the handle of the circuit breaker.

9, 919 represent each a combined overload and underload relayhaving an overload armature l0 and an underload armature 1.1 each provided With a retracting spring" as indicated.

12 is a metallic bracket rigidly mounted on the insulating panel 13 in. position to form contact through the magnet frame for either the overload or the underloed armature. The control circuit for the trip coil 6 is normally open, and may be completed by either or": these armatures, the trip circuit including the Wire 1% connecting in parallel Wibl'lihfi brackets 12 of the several relays, and connecting with one of the contacts bridged by the handle of the circuit breaker.

151's a wire connectir with one of the motorleads andvin paral e1 relatlon to the,

several relay frames.

rue

and thereby intr eas'es the calibration of the overload armature. The underload ar1na-1 ture, however, is drawn up so as to close this alr gap, thereby mproving the magnetic circuit and permitting the circuit breaker to respond to it rated overload. The flexibility of the bridging contacts 16 of the circuit breaker permits a'small range of movement for the operating handle after closure of the circuit. Therefore, the trip circuit will be completed at 8, a short interval of time after this motor circuitv is closed, and the large starting current'will not lift the overload armature'iOas its niagneticcircuit is weaker than iri running cond itions because of the air gap. This the motor will not open the breaker, butthe magnetic circuit is suliiciently good to draw up the armature 11 and place the relays in roper condition to" actuate the overload trips at their proper cali-,

brated load. When the contact is made a-t 8 the unde'rload armature is agalnst its backstop, and the circuit of the trip coil is closed I through armature ll ,but the latter starts on its forward excursionand-. 'open-circuits the coil instantlyand before the operator .can

release his grip of the handle, after whichthe latch'of the breaker drops into its seat and holds the breaker closed, and during this interval the overload armature cannot be raised, owing to the high reluctance of its magnetic circuit. If. desired, the underload armature: may be retarded in f.'n' vardmove ment as] .af'small da'shpot to produce a longer time hmlt for the protection. If an overload should occur under running conditions one of the, armatures 10, according to the line in whichjthe overload'occurs, will be raised, closing the trip circuit and opening the switch which supplies the motor. The circuit may be traced as follows: from line 7, overload trfip coil 6, contact 8, conductor 14, any or all relay joverload" armatures (when raised by overload) relay frame to outside motor leads. wires should break, the underload armature corresponding to that'li'ne opens and closes the circuit to the trip magnet over the circuit 7, 6, 8, 14: and 15, including the armature of the line affected. In case of failure of voltage on" all the lines the motor will supply the tripping current, or, if desired, this trip circuit may be. fed from a local source instead of the motor leads.

Having thus described my invention, I declare that what I claim as new and desire t obtain by Letters Patent, is:

1. Means for protecting counter electro- ''If either of the lineline, said circuit breaker ha- -..1g its trip coil in a normally open circuit, and overload and underload relay armatures for closing the circuit of the trip coil, the underload or mature in its retractedposition increasing the'reluctance of the magnetic circuit of the overload armature to prevent tripping the.

circuit breaker, under starting load.

3. Means for protecting electric motors comprising a circuit breaker having a trip coil and adapted to connect the motor with line, a normally open circuit including the trip coil,.and a combined underload and overload relay in the motor circuit adapted to close thetrip circuit of the circuit breaker, said relay having a common magnetic circuitfor the overload and underload armatures, the underload armature when retract ed producing an air gap in said magnetic circuit to prevent tripping the circuit breaker when the motor is started.

' 4. Means for protecting electric motors comprising'a circuit breaker having a trip coil, a

cuit, and an auxiliary switch governed by the circuit breaker for closing the trip circuit when the circuit breaker is cramped into latching position.

5. Means for protecting counter electro motive apparatus, taking a larger starting than running current, comprising a circuit breaker having electro-responsive"tripping means and adapted to connect said a paratus with the source of supply, a relay aving overload and underload armatures controlling said tripping means, the said underload armature preventing operation of said overload armature by starting current.

6h The ombinationwith a polyphase motor, of a circuit breaker adapted to establish circuits through said motor when closed and to interrupt current therethrough when it is open, said circuit breaker comprising an electro-responsive tripping device, and means for opening said circuit breaker upon overload or. underload in any of the phases of said motor, s'aid means comprising a 011- cuit controlling said tripping device and a plurality of relays controlling the last men tioned circuit, said relays being connected to be operated on underload or overload in any phase, each of said relays comprising acoil,

an underload armature and an overload armature, the said underload armature preventing operation of the overload armature by starting current.

In festimon fihereof a iii x my signature, in presence-o two witnesses GIEJORGE AUGUSTUS BURNHAM. Witnesses: I

A: C. NELSON,

H. CALDER. 

